On Saturday I travelled Along the Central Line for a short while, from West Ruislip to Northolt. It was fine.
This picture is taken from the Eastbound platform at Northolt. It is possible to make out the over-bridge station building, which is also where the main A412 crosses the railway.
Running parallel to the Central Line is a little used single track railway line. It runs from Northolt Junction, has a triangular junction at Greenford and then continues on to the Paddington main lines just East of North Acton station. The line used to be double tracked - I think there is a passing loop somewhere just East of Greenford.
The current plans for High Speed 2 involve the entire stretch of parallel line being part of the route from Euston to Birmingham.
There are all sorts of contentious aspects to the HS2 plans - tunneling underneath grumpy people on the route from Euston and carving up parts of the Chiltern Hills, never mind burning truckloads of money that we don't have.
To give some idea of the work involved, never mind the impact on those living nearby, imagine what will be needed to upgrade this single bridge (and probably the entire underground station building) to allow two high speed (up to 400 kph / 250 mph) tracks to pass through the area highlighted. Simply mind boggling.